The present invention relates to an exhaust system for a small internal combustion engine, and more particularly to a catalytic converter for two or four-cycle engines of the type having one or two cylinders having an arrangement for introducing secondary air into the catalytic converter.
In order to reduce harmful hydrocarbons, carbon monoxide and nitrous oxide components in exhaust gas, it is known to utilize a catalytic converter containing a catalyzer disposed in the exhaust system of the engine upstream of a muffler. It is also known to feed secondary air into the exhaust system upstream of the catalytic converter for promoting oxidation of unburned hydrocarbons and carbon monoxide components in the exhaust gas to thereby reduce the expelling of such harmful components into the atmosphere.
The secondary air supply system generally comprises one of two different designs. The first type is an engine driven air pump such as a belt driven vein pump mounted to a conventional internal combustion engine to inject compressed air into the exhaust manifold of the engine by way of an air injection manifold. Alternately, it is also been proposed to utilize exhaust gas pulsation in the exhaust manifold of automobile engines for injecting secondary air into the exhaust system upstream of a catalytic converter. In particular, it is known to utilize atmospheric air as the secondary air to be introduced upstream of a catalytic converter in the exhaust system by using a reed-type check valve which is operated by the action of exhaust pressure pulsations generated in the exhaust manifold. The engine driven air pump has the advantage that it is capable of supplying any variable quantity of secondary air into the exhaust system while the system employing exhaust gas pulsation to produce the pumping action has the advantage that the supply of secondary air is obtained by a relatively simple and inexpensive structure.